8 #include <cdsannotate.h>
9 #include <specannotation.h>
10 #include <model_memory.h>
14 std::atomic<mcs_node *> next;
15 std::atomic<int> gate;
26 // tail is null when lock is not held
27 std::atomic<mcs_node *> m_tail;
38 //ASSERT( m_tail.load() == NULL );
41 // Each thread will have their own guard.
45 mcs_node m_node; // node held on the stack
47 guard(mcs_mutex * t) : m_t(t) { t->lock(this); }
48 ~guard() { m_t->unlock(this); }
60 _lock_acquired = false;
69 @Commit_point_set: Lock_Enqueue_Point1 | Lock_Enqueue_Point2
71 _lock_acquired == false;
73 _lock_acquired = true;
76 void lock(guard * I) {
77 mcs_node * me = &(I->m_node);
80 // not published yet so relaxed :
81 me->next.store(NULL, std::mo_relaxed );
82 me->gate.store(1, std::mo_relaxed );
84 /** Run this in the -Y mode to expose the HB bug */
85 // publish my node as the new tail :
86 mcs_node * pred = m_tail.exchange(me, std::mo_acq_rel);
89 @Commit_point_define_check: pred == NULL
90 @Label: Lock_Enqueue_Point1
95 // unlock of pred can see me in the tail before I fill next
97 // publish me to previous lock-holder :
98 // FIXME: detection miss, execution never ends
99 // If this is relaxed, the store 0 to gate will be read before and
100 // that lock will never ends.
101 pred->next.store(me, std::mo_release );
102 //printf("lock_miss1\n");
104 // (*2) pred not touched any more
106 // now this is the spin -
107 // wait on predecessor setting my flag -
108 rl::linear_backoff bo;
111 my_gate = me->gate.load(std::mo_acquire);
113 //printf("lock at gate!\n");
116 @Commit_point_define_check: my_gate == 0
117 @Label: Lock_Enqueue_Point2
129 Unlock_Point_Success_1 | Unlock_Point_Success_2
131 _lock_acquired == true
133 _lock_acquired = false;
136 void unlock(guard * I) {
137 mcs_node * me = &(I->m_node);
139 // FIXME: detection miss, execution never ends
140 mcs_node * next = me->next.load(std::mo_acquire);
141 //printf("unlock_miss2\n");
144 mcs_node * tail_was_me = me;
146 success = m_tail.compare_exchange_strong(
147 tail_was_me,NULL,std::mo_acq_rel);
150 @Commit_point_define_check: success == true
151 @Label: Unlock_Point_Success_1
156 // got null in tail, mutex is unlocked
160 // (*1) catch the race :
161 rl::linear_backoff bo;
163 // FIXME: detection miss, execution never ends
164 next = me->next.load(std::mo_acquire);
165 //printf("unlock_miss3\n");
172 // (*2) - store to next must be done,
173 // so no locker can be viewing my node any more
176 next->gate.store( 0, std::mo_release );
179 @Commit_point_define_check: true
180 @Label: Unlock_Point_Success_2